In the current art, communications signals are regularly transported through networks via optical transmission arrangements in order to take advantage of the larger bandwidth available with optical signals transported over fiber optic media. In simple terms, such optical transport is effected by conversion of an electrical signal to be transmitted into a light signal through the use of a Laser Driver and laser diode which is interfaced to a fiber optic cable. At the receiving end, the transmitted light signal is converted back to an electrical signal by a photo diode. In practice, a Laser Driver (and associated electronics) is usually arranged in combination with a photo diode (and its associated electronics) into an opto-electronic transceiver module for providing two-way communication at a deployed location.
Opto-electronic transceiver modules provide for the bi-directional transmission of data between an electrical interface and an optical data link. The module receives electrically encoded data signals that are converted into optical signals and transmitted over the optical data link. Likewise, the module receives optically encoded data signals that are converted into electrical signals and transmitted onto the electrical interface.
In response to increasing demand for network channel capacity, as well as cost constraints, a Small Form Factor (SFF) standard evolved during the 1990s to reduce the size of many networking components. One such component, an SFF opto-electronic transceiver and its associated connector, mates with a receptacle in an equipment panel that is approximately the size of an RJ-45 jack (and approximately one-half the size of the prior connection arrangement). Thus, a considerably higher port density for fiber terminations can be achieved with the use of SFF opto-electronic transceivers.
The SFF standard for opto-electronic transceivers specifies minimum transceiver functionality and spells out transceiver physical dimensions. The module dimensions result in tight size constraints for the transceiver components. The receive part of the transceiver typically uses a photodiode (which converts an input light signal to an output current) combined with a transimpedance amplifier (TIA) to convert the photodiode output into a voltage for further processing and data recovery. The photodiode and TIA are usually mounted together in a package known as a “TO” can in order to keep the parasitic capacitance and inductance to a minimum for high data-rate transmission systems (e.g., 2.5 Gb/s and higher data rates). That combination of photodiode and TIA mounted in a TO-can will be referred to herein from time to time as the “receive module.”
The TO-can must be small to fit inside the SFF transceiver, and this size constraint severely limits the TO-can pin count. The photodiode of the receive module is usually either a PIN diode or an avalanche photo diode (APD). Most PIN diode applications use 4-pin TO-cans and APD diode applications use 5-pin TO-cans.